From what you've described it sounds like the timing is ramping up too quickly. If the springs are too light resulting in too much advance for the engine load, it'll ping. However before changing anything, like others have mentioned, check & record the timing profile. I hope they sold you a dist specifically for a Firebird and it isn't configured for a different application?

I have a harmonic balancer with degree marks up to 90 deg. So with my handy old-school timing light I record the timing at every 200 rpm until it stops advancing. I'm currently running a hop-out curve [vs. a linear curve] which a fast and then slow ramp, (per Hot Rod less advance is needed as piston speed increases). If I recall mine is fast from 1000 - 1800 rpm and then slow up to ~3400, with initial at 9-10. I tried to run 12-13 initial and would get what sounded like valve-train noise in 2nd & 3rd gear at cruise. If you run the initial too low, it'll be harder to start and run hotter. I've seen many ponchos with the paint burned off the heads.

Perhaps some of the older readers remember back when you could take a new distributor to your local speed shop and they'd set it up for you. They just needed the weight of the car, and drive-train info. You can't find that service anymore...